He was one of mankind's last four survivors in an apocalyptic future, along with Z-one, Aporia and Antinomy. Unlike his fellow survivors, not much of his backstory prior to meeting the other survivors is shown.
His name is derived from the concept of "paradox" in the theory of time. According to it, a paradox is created if the past is altered which then changes the future entirely. This references his mission of changing history by destroying the game of Duel Monsters to prevent his own terrible future from happening, which would have caused catastrophic and drastic changes to the future had he succeeded
He is the only one of Z-one's comrades to not guard a Planetary Particle as he was defeated before then. Sherry LeBlanc replaces him as the third guard of a Planetary Particle.
Paradox was one of the survivors of the "Meklord Emperor" genocide along with Z-one and Antinomy, who eventually discover a fourth survivor, Aporia. Together, the four of them had conducted many experiments in order to prevent the genocide, but he alongside Antinomy and Aporia eventually died from natural causes and were placed in capsules, leaving Z-one the only survivor.
A robotic copy of Paradox's younger self was made by Z-one and was sent back in time in an attempt to rewrite history and create a better future, by eliminating the creator of Duel Monsters, Maximillion Pegasus.
If the popularity of Duel Monsters fell, it would cause a domino effect on the timeline, resulting in none of the Duel Academies ever being founded to inspire the following generations to pursue even greater achievements, such as New Domino City, Turbo Duels and Ener-D. Even worse, lives would be snuffed out by the changes; if couples were brought together by Duel Monsters, then the new timeline would result in the lack of offspring had by the couples.
Paradox was fully aware of this consequence, but believed it was necessary as many great evils that threatened the world (Yami Marik, The Great Leviathan, Zorc, the Shadow Riders, The Light of Destruction,Nightshroud, the Dark Signers, etc) used Duel Monsters in their attempt to destroy it. He overlooked that if Duel Monsters didn't exist, the evil beings would have tried different ways to accomplish their plans; at least with Duel Monsters, the chance to fight back was fair.
Paradox traveled to the New Domino City, during Yusei Fudo's time. He interrupted a Turbo Duel between Yusei, Crow Hogan and Jack Atlas. Yusei has just Summoned "Stardust Dragon", but Paradox absorbed it into a blank card. He showed Yusei the corrupt card, when confronted, before vanishing through time again.
He traveled further back in time to Venice, during Jaden Yuki's time. Causing massive destruction, Paradox attacked Jaden with "Cyber End Dragon" and "Rainbow Dragon". Elemental Hero Neos protected Jaden, so Paradox Summoned "Stardust Dragon" to fight off "Neos". However, Yusei who has traveled back in time with help from the Crimson Dragon arrived and saved Jaden. Though unsure of how Yusei followed him back into the past, Paradox decides to let the alterations to the timeline finish him and Jaden off.
Paradox proceeded to visit an event where Pegasus was giving cards to young children, in Yugi Muto's time, where he used "Cyber End Dragon," "Rainbow Dragon" and "Stardust Dragon" to attack the area. Obsessed with the utter destruction of the "plague" that destroyed his home time, Paradox cared little for the other people in the area, killing them along with Pegasus and Solomon Muto with a falling building. Yusei and Jaden arrived in this time and recruited Yugi, who was the lone survivor of Paradox's attack, to fight Paradox.
Yusei, Jaden and Yugi traveled back in time to exactly thirty minutes before Pegasus' event and confronted Paradox before he could attack the crowd again. He faced them in a 3-on-1 Duel. Paradox used "Malefic World" and his corrupt "Malefic" counterparts of existing monsters. Yusei, Jaden and Yugi managed to retrieve "Stardust Dragon" from him, and by combining it with their cards, they destroyed Paradox's "Malefic Truth Dragon" and won the Duel, which destroyed Paradox in the process.
Z-one later mentioned Paradox when explaining his plans to Team 5D's, and Yusei recognizes his name and remembers his encounter with him. Z-one revealed that it was him who had sent Paradox to the past. Before he died, Z-one said that by remembering Paradox, Antinomy and Aporia's bond he was able to find the strength to fight by himself, and that he considered the three to be his family.
Paradox possesses a Duel Runner that bears similarities to the one used by Aporia. The Duel Runner is shown to travel through time and change between modes. Like Yusei's Duel Runner, Paradox possesses a hybrid model.